In the following description, the terms ‘crane’ and ‘hoisting machine’ or ‘hoisting apparatus’ are used as synonyms. Correspondingly, the term ‘hook’ is used to refer to all types of load-fixing means. In this description, ‘down’ means, as usual, the direction in which gravitation tends to draw mass, and ‘up’ is the direction opposite to gravitation. In connection with elements of a crane, ‘up’ and ‘down’ refer to the normal operating state of the crane. For instance, a conventional hook is said to open upwards and to be closed in the lower part even if the hook were, in some cases, in a position deviating from its normal position. In a crane having a trolley which moves supported by a horizontal girder, i.e. a bridge, and from which a sheave carrying the hook is suspended via a rope or chain, supplying power in connection with the hook is difficult because the hook moves vertically relative to the crane trolley and horizontally when the trolley and the bridge are moving in lateral directions. If power supply is required for the hook or some other type of catch, the cable used is custom-made and thus expensive. The cable is also sensitive to wearing and stress. Also with regard to its structure, such a solution is expensive and difficult to implement, although such solutions are used when required, particularly in large cranes. There would be many applications for power supply in connection with a hook, also in smaller cranes in which providing power supply in connection with the hook would be unreasonably expensive proportioned to the price of the crane.
Publication DE10001215A1 discloses a dynamo supplying current to a radio transmitter at the end of a telescopic crane jib. The dynamo is mounted radially on a rigid structure in a manner known from bicycles but this structure extends and retracts telescopically.
Publication DE 102004027106A1 discloses a sensor to be mounted on a gearbox above the crane hook for weighing the load. Publications DE102009036480A1 and U.S. Pat. No. 5,071,184 also disclose various techniques for supplying energy to crane structures.
However, applying known structures to cranes involves some particular problems. There are certain problems in the techniques disclosed in the above references. For example when the crane hook is supported against the crane frame via a flexible structure, such as a cable or chain, supplying energy to the hook from fixed structures of the crane is remarkably cumbersome.
Further, for instance in connection with bicycles, it is generally known to generate current locally, for instance by using a dynamo connected to a bicycle wheel via frictional force. If energy is generated by a generator connected to a sheave radially in the same way as a bicycle dynamo, the structure easily gets dirty and is sensitive to moisture and freezing, in which case the risk is that in wintertime the dynamo will not rotate or generate current.
Further, the use of a crane is irregular by nature, so the sheaves do not rotate continuously either. Energy may be needed in connection with a hook or generally in connection with sheaves even between the operating moments of the crane. If it were desirable to exploit energy in a working lamp mounted in connection with a hook, for example, it would not be reasonable for the working lamp to work only when the hook is rising or lowering. Yet another particular problem is that the vertical movement of a crane hook is extremely slow compared with, for instance, the speed of a bicycle. A bicycle typically moves about 6 meters per second (about 20 km/h), whereas the vertical speed of a crane hook is typically 6 meters per minute. Despite this, a bicycle dynamo contains transmission with which the rotation speed of the dynamo is increased compared with the rotation speed of the wheel in proportion to the radii of the rims, i.e. about 50-fold. The rotation speed of a crane sheave thus barely reaches one percent of the rotation speed of a bicycle dynamo.
Generating usable output power from the movement of a crane sheave is thus, to say the least, challenging. Transmission based on frictional force would, per se, provide an easy way to increase the rotation speed of a generator but a problem is, for example, the loss of frictional force caused by freezing and the resulting locking of the dynamo. Thus, when the structure freezes, the dynamo will not rotate or generate energy. On the other hand, with rigid connection of the generator to the sheave, the rotation speed of the generator remains as low as the revolution speed of the sheave, which is typically only a few revolutions per minute.